Solid-state image pickup device

ABSTRACT

A solid-state image pickup device is provided which can inhibit degradation of image quality which may occur when a global electronic shutter operation is performed. A gate drive line for a first transistor of gate drive lines for pixel transistors is positioned in proximity to a converting unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application is Continuation of U.S. application Ser. No.15/498,197, filed Apr. 26, 2017, which is a Continuation of U.S.application Ser. No. 15/040,727, filed Feb. 10, 2016, now becomes U.S.Pat. No. 9,666,633, issued on May 30, 2017, which claims priority fromJapanese Patent Application No. 2015-027924, filed Feb. 16, 2015, whichare hereby incorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to positioning of drive lines in asolid-state image pickup device.

Description of the Related Art

In recent years, image pickup devices such as a digital camcorder and adigital camera applying a CMOS image sensor suitable for low powerconsumption and high speed readout have been generally available. A CMOSimage sensor having a plurality of pixels each containing aphotoelectric converting unit arranged in row and column directions isproposed which is configured as a global electronic shutter in which anexposure start and an exposure end are electronically controlledsimultaneously in all of the pixels (International Publication No. WO11/043432).

SUMMARY OF THE INVENTION

A device according to an aspect of the present invention having an imagesensing region in which a plurality of pixels are arranged in a matrixform, each of the pixels having a converting unit, a first transistorconfigured to transfer electric carriers in the converting unit, anaccumulating portion configured to accumulate electric carrierstransferred from the first transistor, a second transistor configured totransfer electric carriers from the accumulating portion, a floatingdiffusion (hereinafter, called an FD) configured to accumulate electriccarriers transferred from the second transistor, and a reset transistorconfigured to reset a potential of the FD includes gate drive lines fora plurality of pixel transistors configured to drive gates of the pixeltransistors each including the first transistor, the second transistor,and the reset transistor, the gate drive lines extending in a directionof rows of the pixels in one wiring layer. In this case, a gate driveline for the first transistor among the gate drive lines for the pixeltransistors is positioned in proximity to the converting unit in drivingwiring of rows (n−1), rows (n), and rows (n+1) provided correspondinglyto rows of the pixels.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating pixels according to a firstembodiment of the present invention.

FIG. 2 is a cross section view of pixels according to the firstembodiment of the present invention.

FIG. 3 is a pixel circuit diagram according to the first embodiment ofthe present invention.

FIG. 4 is a driving timing chart according to the first embodiment ofthe present invention.

FIG. 5 is a plan view of pixels according to a second embodiment of thepresent invention.

FIG. 6 is a cross section view according to the second embodiment andthird and fourth embodiments of the present invention.

FIG. 7 is a pixel circuit diagram according to the second, third andfourth embodiments of the present invention.

FIG. 8 is a driving timing chart according to the second, third andfourth embodiments of the present invention.

FIG. 9 is a plan view of pixels according to the third embodiment of thepresent invention.

FIG. 10 is a plan view of pixels according to the fourth embodiment ofthe present invention.

FIG. 11 is a schematic diagram regarding an example of arrangement ofdriving wiring according to the first embodiment of the presentinvention.

FIG. 12 is an explanatory diagram of a wiring distance.

FIG. 13 is a schematic diagram regarding an example of arrangement ofdriving wiring according to the second embodiment of the presentinvention.

FIG. 14 is a schematic diagram regarding an example of arrangement ofdriving wiring according to the third embodiment of the presentinvention.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

A first embodiment of the present invention will be described withreference to FIG. 1 to FIG. 4 and FIG. 11. FIG. 1 is a plan view of aplurality of pixels arranged in a 3×3 matrix form. FIG. 2 is a crosssection view of pixels of a part taken at line II-II in FIG. 1. FIG. 3is an equivalent circuit diagram illustrating pixels in three rows andthree columns corresponding to FIG. 1. FIG. 4 is a driving timing chartfor operating a solid-state image pickup device according to thisembodiment. Like numbers refer to like parts throughout. Positive holesmay be used as signal electric carriers though a configuration in whichelectrons are used as signal electric carriers will be described below.When positive holes are used as signal electric carriers, theconductivity type of semiconductor regions may be opposite to theconductivity type in a case where signal electric carriers areelectrons.

Referring to FIG. 3, each of pixels P1 includes a first transfertransistor 14 configured to transfer electric carriers in aphotoelectric converting unit 1, and an electric carrier accumulatingportion 3 configured to accumulate electric carriers transferred fromthe first transfer transistor 14. Each of the pixels P1 further includesa second transfer transistor 15 configured to transfer electric carriersfrom the electric carrier accumulating portion 3. Each of the pixels P1further includes a floating diffusion 6 (hereinafter, called an “FD 6”)configured to accumulate electric carriers transferred from the secondtransfer transistor 15, a reset transistor 16 configured to reset thepotential of the FD 6, a source follower transistor 17, and a rowselection transistor 18.

Each of the pixels P1 is connected to a vertical output line Voutthrough a pixel output unit 22. A power supply 20, and a ground 21 arefurther provided therein. According to this embodiment, a configurationcalled a Vertical Overflow Drain (hereinafter, VOFD) is provided inwhich electric carriers are output from the photoelectric convertingunit 1 to the semiconductor substrate 7 through an embedded layer 9.

FIG. 2 is a pixel cross section view taken at line II-II in FIG. 1. Ap-type embedded layer 9 and a p-type well 8 are provided on an n-typesemiconductor substrate 7. The surface protective layer 2 is provided onthe photoelectric converting unit 1 having the n-type and the p-type sothat a so-called buried type photodiode can be configured. A p-typesurface protective layer 4 is provided on an n-type electric carrieraccumulating portion 3.

A depleting inhibiting portion 5 is provided under the p-type electriccarrier accumulating portion 3, and the depleting inhibiting portion 5is made of a higher density semiconductor than that of the well 8.

Supply of pulses which turns on the first transfer transistor 14 to TX1being a gate of the first transfer transistor 14 causes electriccarriers in the photoelectric converting unit 1 to be transferred to theelectric carrier accumulating portion 3.

Supply of pulses which turns on a second transfer transistor 15 to TX2being a gate of the second transfer transistor 15 causes electriccarriers accumulated in the electric carrier accumulating portion 3 tobe transferred to the FD 6.

Next, with reference to FIGS. 3 and 4, operations to be performed by thesolid-state image pickup device according to this embodiment will bedescribed. Referring to FIG. 4, transistors having a low level(hereinafter, called an L level) have a non-conductive state, andtransistors having a high level (hereinafter, called an H level) have aconductive state.

Referring to FIGS. 3 and 4, pTX1(n) indicates a gate drive line of thefirst transfer transistor 14 of an nth row, and pTX2(n) indicates a gatedrive line of the second transfer transistor 15 of the nth row. pRES(n)indicates a gate drive line of the reset transistor 16 of the nth row,and pSEL(n) indicates a gate drive line of the row selection transistor18 of the nth row. A number within each of the parentheses after namesof gate drive lines indicates the row number of pixels.

At a time t0 in FIG. 4, the level of the substrate potential is changedto an L level so that VOFD is turned off. Thus, accumulation ofelectrons having undergone photoelectric conversion in the photoelectricconverting unit 1 is started.

Next, at a time t1, the levels of the gate drive lines pTX1(n−1),pTX1(n), and pTX1(n+1) for the first transfer transistors 14 are changedto an H level so that the first transfer transistors 14 are turned on.Thus, electrons are transferred to the electric carrier accumulatingportion 3. After a lapse of a predetermined time period, the firsttransfer transistors 14 are turned off so that the transfer of electronsto the electric carrier accumulating portions 3 ends.

Because the electric carrier accumulating portions 3 are provided inthis embodiment, signal electric carriers in the photoelectricconverting units 1 in all pixels are simultaneously transferred to theelectric carrier accumulating portions 3. This can implement anoperation to be performed by a global electronic shutter which controlsan exposure start and an exposure end simultaneously in all pixelsthrough an electronic switch.

Next, at a time t2, the level of the substrate potential is changed toan H level so that a punch-through occurs between the photoelectricconverting units 1 and the semiconductor substrate 7. Thus, electriccarriers are output to the semiconductor substrate 7.

The period from the time t0 when VOFD is turned off to the time t1 whenthe first transfer transistors 14 are turned on may be set as requiredso that an image for an arbitrary accumulation time can be obtained.

The first transfer transistors may be turned on a plurality of number oftimes intermittently between the time t0 and the time t1. The turning ona plurality of number of times can reduce the signal electric carriersto be handled by one transfer operation and can facilitate the transferoperation. In a case with the turning on a plurality of number of times,the time t1 is a time for the last one of the plurality of ONoperations.

Next, at times t3, t4, and t5, the level of the gate drive line pTX2 ofthe second transfer transistor 15 is changed to an H levelline-sequentially so that the second transfer transistor 15 is turnedon. Thus, signal electric carriers are transferred from the electriccarrier accumulating portion 3 to the FD 6.

A conventional method for a CMOS image sensor is applicable as a signaltransfer method for the FD 6 and subsequent stages. In other words,signals are output to the vertical signal lines via the source followertransistor 17, the row selection transistor 18, and the pixel outputunit 22. A signal of a noise component may be output to the verticalsignal line before the second transfer transistor 15 is turned on.Though the row selection transistor 18 is provided in FIG. 3, aconfiguration without the row selection transistor 18 may be applied.

The gate drive lines here are made of conductors to transmit drivepulses illustrated in FIG. 4, and a parasitic capacitance is formedbetween the conductors. The parasitic capacitance and an electricresistance of the conductors cause a propagation delay between drivepulses being transmitted through the conductors. As the number of pixelsin the solid-state image pickup device increases, the size of the imagesensing region increases. Thus, the image sensing region may have a parthaving a smaller propagation delay and the other part having a largerpropagation delay. As a result, this may cause differences in operatingtiming of drive pulses to be input to the gates of transistors in pixelswithin the image sensing region, which causes differences in timing forstoring image signals accumulated in the photoelectric converting units1. This may result in degradation of image quality.

With a conventional line-sequential shutter instead of a globalelectronic shutter, differences in accumulation timing within a screenmay not be a significant problem in image quality because there arerelatively large differences in accumulation timing within the screen.However, with a global electronic shutter, because a difference inaccumulation timing for each row may not occur easily, the degradationof image quality due to the difference in accumulation timing caused bya propagation delay may be significant within an image sensing region.The ratio of a difference in accumulation timing to an accumulation timeincreases as the accumulation time decreases. Thus, the differencebecomes more significant, which may possibly be one factor whichprevents reduction of the accumulation time.

The accumulation timing in a global electronic shutter is controlled bythe first transfer transistors 14 as described above. Thus, theparasitic capacitance of the gate drive line pTX1 for the first transfertransistor 14 may be reduced to reduce the propagation delays so thatthe difference in accumulation timing can be reduced within the imagesensing region. Such an influence of the parasitic capacitance maysignificantly occur in a case where gate drive lines for a plurality ofpixel transistors are provided within one wiring layer and the gatedrive lines are positioned closely.

Positioning of pTX1

Next, with reference to FIG. 1, positioning of drive lines for pixeltransistors for reducing parasitic capacitance of the gate drive linepTX1 will be described.

FIG. 1 illustrates semiconductor regions, gate electrodes of pixeltransistors and wiring for electrically connecting the semiconductorregions and the gate electrodes of the pixel transistors in thephotoelectric converting unit 1. In the solid-state image pickup device,lines including a power supply line, a ground power supply line, and avertical output line in addition to the drive lines for pixeltransistors are placed in a wiring layer including a plurality of layersas required. FIG. 1 illustrates the drive lines for pixel transistorsplaced within one wiring layer. For example, in a wiring layer having athree-layer structure, the drive lines for the pixel transistorsillustrated in FIG. 1 are placed in the second wiring layer.

Referring to FIG. 1, gate drive lines for the first transfer transistor14, second transfer transistor 15, and reset transistor 16 are providedon the electric carrier accumulating portion 3 so as to extend in therow direction of the image sensing region. Those gate drive lines arearranged in a periodical layout pattern.

The gate drive line pRES(n) for the reset transistor 16 is only providedin proximity of the gate drive line pTX1(n) and far away from the gatedrive line pTX2(n+1) for the second transfer transistor 15. In thisarrangement, pTX1(n) can have a lower parasitic capacitance comparedwith an arrangement in which gate drive lines for pixel transistors areclosely provided on both sides of pTX1(n).

FIG. 11 schematically illustrates the arrangement of driving wiringillustrated in FIG. 1. Dx indicates a distance between drive lines.

It is assumed here that the total of a wiring distance between a gatedrive line for a first transfer transistor and gate drive lines forpixel transistors provided on both sides of the gate drive line for thefirst transfer transistor in the driving wiring of the rows (n−1), therows (n), and rows (n+1) is equal to DTX1 _(Total).

Similarly, the totals of a wiring distance between a gate drive line forother pixel transistors excluding the first transfer transistor and gatedrive lines for the pixel transistors provided on both sides of the gatedrive line are equal to DTX2 _(Total) for a second transfer transistor,DRES_(Total) for a reset transistor, and DSEL_(Total) for a rowselection transistor.

In this case, DTX1 _(Total) is a value higher than all of DTX2 _(Total),DRES_(Total), and DSEL_(Total).

Referring to FIG. 11, it is assumed that the intervals between drivelines of rows (n−1), rows (n), rows (n+1) are equal to D₁ to D₁₁,respectively.

Here, in the driving wiring of the rows (n−1), rows (n), and rows (n+1),DTX1 _(Total) is equal to D₁+D₃+D₆+D₈+D₉. On the other hand DRES_(Total)is equal to D₁+D₂+D₇+D₈+D₉+D₁₀. DSEL_(Total) is equal toD₂+D₄+D₅+D₇+D₁₀+D₁₁.

Because D₃ and D₆ are three times or more of the interval between otherlines, for example, DTX1 _(Total) is equal to a value higher thanDRES_(Total) and DSEL_(Total) in rows (n−1), rows (n), and rows (n+1).It should be noted that the wiring distance between drive lines isdefined herein by a distance between an end portion of pTX1(n) and anend portion of pRES(n), for example, as illustrated in FIG. 12.

According to the configuration as described above, the parasiticcapacitance occurring in the gate drive line pTX1 can be reduced, and asmaller propagation delay as a result can reduce the differences inaccumulation timing.

The positioning of drive lines as described above can be applied notonly to front side illumination (FSI) but also back side illumination(BSI). Also for back side illumination, it is assumed that drive linesfor pixel transistors are placed correspondingly to rows of pixels.Thus, the drive line positioning example as described above may beapplied in that case.

FIG. 1 illustrates a plan view of pixels of front side illumination. Infront side illumination, a drive line for each pixel transistor isgenerally arranged in a region without a photoelectric converting unit.For example, referring to FIG. 1, a gate drive line for each pixeltransistor is placed on the electric carrier accumulating portion.Therefore, in consideration of the layout of drive lines, the gate driveline pTX1 of gate drive lines for pixel transistors are arranged inproximity of the photoelectric converting unit 1 for the purpose ofreduction of parasitic capacitance of the gate drive line pTX1 for thefirst transfer transistor 14. As a result, the gate drive line pTX1 isplaced at an end portion of the drive line region, and the gate driveline pTX1 has a conductor only in one side of the drive line region.

Positioning of pTX1 and pTX2

According to this embodiment, the gate drive line pTX1 and the gatedrive line pTX2 are not positioned in proximity of each other. Theexpression “not positioned in proximity of each other” refers to apositional relationship in which pTX2 is not placed on both sides ofpTX1. Alternatively, even in a case where pTX2 is placed on one side ofpTX1, the distance between pTX1 and pTX2 is three times or more, forexample, of the distance between pTX1 and a drive line placed on theother side of pTX1.

Problems involved in a case where the gate drive line pTX1 and the gatedrive line pTX2 are placed in proximity of each other will be describedbelow.

When the gate drive line pTX1 and the gate drive line pTX2 havecapacitive coupling, the potential of the gate drive line pTX2 may havea fluctuation when the level of the gate drive line pTX1 changes. Forexample, at the time t1 illustrated in FIG. 4, the level of the gatedrive line pTX2 is originally an L level. However, when the gate driveline pTX1 is changed from an L level to an H level, the potential of thegate drive line pTX2 is changed from an L level to an H level. Thislowers the potential barrier from the electric carrier accumulatingportion 3 to the FD 6. Thus, the saturation signal amount in theelectric carrier accumulating portion 3 can be reduced. The influence ofthe potential fluctuations depending on the variation of parasiticcapacitance within the image sensing region may cause fluctuations ofthe saturation signal amount in the electric carrier accumulatingportion 3 within the image sensing region. This phenomenon becomes moresignificant when the operation of the gate drive line pTX1 is performeda plurality of number of times intermittently between the time t0 to thetime t1.

In some cases, the gate drive line pTX2 may be set to a negativepotential during a period when the second transfer transistor 15 beingan NMOS has an OFF state. Thus, holes are excited in a channel part sothat re-coupling between electrons and holes can inhibit dark currenteven when electrons occur. If the gate drive line pTX1 and the gatedrive line pTX2 have capacitive coupling here, the potential of the gatedrive line pTX2 changes to be higher and the hole excitation can beinsufficient when the level of the gate drive line pTX1 is changed froman L level to an H level. As a result, the dark current inhibition maypossibly become insufficient.

In order to prevent this, the gate drive line pTX1 and the gate driveline pTX2 are not positioned in proximity of each other according tothis embodiment. Particularly, referring to FIG. 1 and FIG. 11, indriving wiring of rows (n−1), rows (n), and rows (n+1), a maximum wiringdistance of wiring distances between gate drive lines for pixeltransistors can be the wiring distance between the gate drive line pTX1and the gate drive line pTX2.

As understood from FIG. 4, when the first transfer transistor is turnedon, the reset transistor also has an ON state. Thus, a change inpotential of the reset transistor from an L level to an H level if anymay not easily have an influence. Therefore, the gate drive line pREScan be positioned in proximity of the gate drive line pTX1.

The gate drive line pSEL may be positioned in proximity of the gatedrive line pTX1 instead of the gate drive line pRES. This is because,even when the row selection transistor has an OFF state when the firsttransfer transistor is turned on, no transfer path for signal electriccarriers exists if the constant current source has an OFF state and novariations in signals occur within the image sensing region.

Alternatively, a power supply line or a ground line instead of the gatedrive line pRES may be positioned in proximity of the gate drive linepTX1 to inhibit a potential fluctuation. This is because such a powersupply line and a ground line are not directly associated with thetransfer path for signal electric carriers and no variations in signalsoccur within the image sensing region.

According to this embodiment, the FD 6 is provided in each pixel.However, the FD 6 may be shared by a plurality of pixels. Also in thiscase, the gate drive line pTX1 for the first transfer transistor may bepositioned as described above to acquire the same effect. Sharing the FD6 by a plurality of pixels can reduce the number of drive lines so thatthe gate drive line pTX1 for the first transfer transistor can beprovided far away from other drive lines and the parasitic capacitancecan thus be reduced.

Second Embodiment

A second embodiment of the present invention will be described withreference to FIG. 5 to FIG. 8 and FIG. 13. Like numbers refer to likeparts throughout in the first and second embodiments, and detaildescriptions will be omitted. FIG. 5 is a plan view of pixels of threerows and three columns in a solid-state image pickup device according tothis embodiment. FIG. 6 is a pixel cross section view of a part taken atthe line VI-VI in FIG. 5. FIG. 7 is an equivalent circuit diagramillustrating pixels of three rows and three columns corresponding toFIG. 5. FIG. 8 is a driving timing chart for operating the solid-stateimage pickup device according to this embodiment.

This embodiment is different from the first embodiment in that anoverflow transistor is separately provided without applying a VOFDconfiguration. In other words, as illustrated in FIGS. 6 and 7, anoverflow transistor 19 is provided. When a gate OFG of the overflowtransistor is turned on, electric carriers are transferred to a powersupply 20 through a plug 12.

FIG. 8 illustrates a timing chart. At a time t0, the level of the gatedrive line pOFG for the overflow transistor 19 is changed to an L levelso that the overflow transistor 19 is turned off.

Next, at a time t1, the level of the gate drive line pTX1 for the firsttransfer transistor 14 is changed to an H level, and the first transfertransistor 14 is turned ON. Thus, electrons are transferred to theelectric carrier accumulating portion 3. After a lapse of apredetermined time period, the first transfer transistor 14 is turnedoff so that the transfer of electrons to the electric carrieraccumulating portion 3 ends.

Next, at a time t2, the level of the gate drive line pOFG is changed toan H level so that the overflow transistor 19 is turned on. Thus,electric carriers can be output from the photoelectric converting unit 1to the power supply 20 which is an overflow drain.

The period from the time t0 when the change of the level of the gatedrive line pOFG to the L level to the time t1 when the first transfertransistor 14 is turned on may be set as required so that an image foran arbitrary accumulation time can be obtained.

FIG. 13 schematically illustrates an arrangement of driving wiringillustrated in FIG. 5. It is assumed that intervals between drive linesof rows (n−1), rows (n), and rows (n+1) are equal to D₁ to D₁₂,respectively. It should be noted that the interval between pOFG(n−2) andan adjacent drive line is not considered because pOFG(n−2) is a driveline for pixels of the (n−2)th row. pOFG(n+1), not illustrated, is notalso considered because it is positioned between pRES(n+2) andpSEL(n+2).

Here, in rows (n−1), rows (n), rows (n+1), DTX1 _(Total) is equal toD₁+D₃+D₈+D₁₀+D₁₁. On the other hand, DRES_(Total) is equal toD₁+D₂+D₉+D₁₀+D₁₁. DSEL_(Total) is equal to D₄+D₅+D₆+D₇+D₁₂. DOFG_(Total)is equal to D₂+D₄+D₇+D₉.

Because D₃ and D₈ are three times or more of the interval between otherlines, for example, DTX1 _(Total) is equal to a value higher thanDRES_(Total), DSEL_(Total), and DOFG_(Total) in the rows (n−1), rows(n), rows (n+1). According to the configuration, the parasiticcapacitance occurring in the gate drive line pTX1 can be reduced, and asmaller propagation delay as a result can reduce the differences inaccumulation timing.

This wiring arrangement can be expressed as that pTX1 and pTX2 are notpositioned in proximity of each other. Furthermore, the distance betweenpTX1 and pTX2 in rows (n−1), rows (n), and rows (n+1) can be expressedas a maximum wiring distance of wiring distances between gate drivelines for pixel transistors.

Positioning of pTX1 and pOFG

A problem may possibly arise when the gate drive line pTX1 and the gatedrive line pOFG have capacitive coupling. In other words, at a time t1in FIG. 8 when the level of the gate drive line pTX1 is changed from anL level to an H level, the level of the gate drive line pOFG is an Llevel. However, when the gate drive line pTX1 and the gate drive linepOFG have capacitive coupling, the potential of the gate drive line pOFGmay have a change from an L level to an H level at the time t1. Thus,the potential barrier from the photoelectric converting unit 1 to thepower supply 20 being an overflow drain is reduced, and electrons aretransferred from the photoelectric converting unit 1 to the power supply20 so that the saturation signal amount in the photoelectric convertingunit 1 may possibly decrease. This may cause variations of signalswithin the image sensing region.

Accordingly, as illustrated in FIG. 5 and FIG. 13, a drive line pRES isprovided between the gate drive line pTX1 and the gate drive line pOFGin one driving wiring region so that the drive lines are positioned inproximity of each other, according to this embodiment.

This embodiment applies overflow transistors while the first embodimentapplies a VOFD configuration. Application of the deeper photoelectricconverting unit 1 in order to increase the sensitivity on a longerwavelength side makes output of electric carriers difficult with theVOFD configuration. However, also in this case, overflow transistors maybe applied so that electric carriers can be output. In the VOFDconfiguration, a punch-through occurs between the photoelectricconverting unit 1 and the semiconductor substrate 7. Thus, the embeddedlayer 9 may be required to be made of a low density semiconductor tosome extent. On the other hand, with application of overflowtransistors, the embedded layer 9 may be made of a high densitysemiconductor. This may improve the sensitivity of the photoelectricconverting unit 1 and improve the efficiency of transfer to the electriccarrier accumulating portion 3.

On the other hand, because application of a VOFD configurationeliminates the necessity for the gate OFG and gate drive line pOFG foran overflow transistor, the empty region may be allocated to othercomponents. For example, the intervals between drive lines can beincreased while keeping the same size of the photoelectric convertingunit 1. Thus, the parasitic capacitance of the gate drive line pTX1 forthe first transfer transistor can be further reduced compared with thefirst embodiment. The area of the photoelectric converting unit 1 may beincreased so that the saturation charge quantity of the photoelectricconverting unit 1 can be increased, and its sensitivity can beincreased.

Third Embodiment

A third embodiment of the present invention will be described withreference to FIGS. 6, 7, 9, and 14. Like numbers refer to like partsthroughout in the first, second and third embodiments, and detaildescriptions will be omitted.

FIG. 9 is a plan view illustrating pixels of three rows and threecolumns in a solid-state image pickup device according to thisembodiment. The third embodiment is different from the second embodimentin the positions where the gate drive line pOFG and the gate drive linepTX2 are provided.

Referring to FIG. 9, the wiring distance between the gate drive linepTX1 and the gate drive line pOFG is a maximum wiring distance of wiringdistances between gate drive lines for pixel transistors. Thisarrangement can reduce not only the parasitic capacitance of the gatedrive line pTX1 and other gate drive lines but also the parasiticcapacitance of the gate drive line pOFG and other gate drive lines.

The accumulation timing with a global electronic shutter can becontrolled also by an input of drive pulses to a gate OFG of theoverflow transistor 19, as described above. Therefore, the parasiticcapacitance of the gate drive line pOFG for the overflow transistor 19can be reduced, and a propagation delay occurring therein can bereduced. As a result, the difference in accumulation timing can bereduced.

According to this embodiment, the gate drive line pOFG and the gatedrive line pTX2 are not positioned in proximity. If they are positionedin proximity, the saturation signal amount in the electric carrieraccumulating portion 3 can be reduced, which may cause variations insaturation signal amount in the electric carrier accumulating portion 3within the image sensing region.

In some cases, the gate drive line pTX2 may be set to a negativepotential during a period when the gate drive line pTX2 for the secondtransfer transistor 15 being an NMOS has an OFF state. Thus, holes areexcited in a channel part, and re-coupling of electrons and holes isthus caused, which can inhibit dark current. If the gate drive line pOFGand the gate drive line pTX2 have capacitive coupling here, thepotential of the gate drive line pTX2 changes to be higher at a timepoint when the level of the gate drive line pOFG is changed from an Llevel to an H level. As a result, the inhibition of dark current maypossibly in sufficient.

Accordingly, a gate drive line pRES for a reset transistor is positionedbetween the gate drive line pOFG and the gate drive line pTX2 in onedriving wiring region. A gate drive line pSEL for a row selectiontransistor, a power supply line, a ground line or the like may bepositioned instead of the gate drive line pRES.

FIG. 14 schematically illustrates an arrangement of driving wiringillustrated in FIG. 9.

In this case, in driving wiring of rows (n−1), rows (n), and rows (n+1),DTX1 _(Total) is equal to D₁+D₃+D₈+D₁₀+D₁₁+D₁₃. On the other hand,DRES_(Total) is equal to D₁+D₂+D₉+D₁₀+D₁₁+D₁₂. DSEL_(Total) is equal toD₄+D₅+D₆+D₇+D₁₄. Furthermore, DTX2 _(Total) is equal toD₂+D₄+D₇+D₉+D₁₂+D₁₄.

Because D₃, D₈, and D₁₃ are three times or more of the interval betweenother lines, for example, DTX1 _(Total) is a value higher thanDRES_(Total), DSEL_(Total), and DTX2 _(Total) in rows (n−1), rows (n),and rows (n+1).

For the reason above, pTX1 and pOFG are not positioned in proximity asillustrated in FIG. 14, pTX2 and pOFG are not positioned in proximity,and pTX1 and pTX2 are not positioned in proximity.

Furthermore, pOFG is positioned in proximity to the photoelectricconverting unit 1.

In addition, as described above, the wiring distance between pTX1 andpOFG is a maximum wiring distance of wiring distances between gate drivelines for pixel transistors.

Fourth Embodiment

A fourth embodiment of the present invention will be described withreference to FIGS. 6 to 8 and FIG. 10. Like numbers refer to like partsthroughout in the first to fourth embodiments, and detail descriptionswill be omitted.

FIG. 10 is a plan view illustrating pixels of three rows and threecolumns in a solid-state image pickup device according to thisembodiment. The fourth embodiment is different from the second and thirdembodiments in that the line width of the gate drive line pOFG and theline width of the gate drive line pTX1 are greater than the line widthof other drive lines. The positions of the drive lines are also changedas required.

A propagation delay of each drive pulse transmitted through a conductorcan be expressed by a product of a parasitic capacitance and an electricresistance of the conductor. Thus, the electric resistance may bereduced to obtain the same effect as the reduction of the parasiticcapacitance. In other words, the line width of the gate drive line pOFGand the line width of the gate drive line pTX1 may be increased toreduce the propagation delays and thus reduce the differences inaccumulation timing.

Having described that according to this embodiment, the line widths ofboth of the gate drive line pOFG and the gate drive line pTX1 areincreased, one of them may only be increased. Alternatively, one of themmay further be increased.

Such a configuration with drive lines having increased line widths mayrequire reduction of the width of a wiring open region where no drivelines are placed or and reduction of the intervals between drive lineswhile keeping the width of the wiring open region. For that, byexamining the effect of the reduction of parasitic capacitance and theeffect of the reduction of electric resistance, one of theconfigurations with a greater effect may be selected.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

What is claimed is:
 1. An imaging device having an image sensing regionin which a plurality of pixels are arranged in a matrix form, each ofthe pixels having a photoelectric converting unit, a first transfertransistor configured to transfer electric carriers in the photoelectricconverting unit, a carrier accumulating portion configured to accumulateelectric carriers transferred from the first transfer transistor, asecond transfer transistor configured to transfer electric carriers fromthe carrier accumulating portion, a floating diffusion configured toaccumulate electric carriers transferred from the second transfertransistor, a reset transistor configured to reset a potential of thefloating diffusion, and an overflow transistor that discharges electriccarriers of the photoelectric converting unit, comprising: a gate driveline for the first transfer transistor; a gate drive line for the resettransistor; a gate drive line for the overflow transistor; and a regionwhere the gate drive line for the first transfer transistor, the gatedrive line for the reset transistor, and the gate drive line for theoverflow transistor extend in a first direction in a planar view,wherein, in the region, a line width of the gate drive line for thefirst transfer transistor and a line width of the gate drive line forthe overflow transistor are greater than a line width of the gate driveline for the reset transistor.
 2. The imaging device according to claim1, further comprising: a selection transistor; wherein a gate drive linefor the selection transistor extends in the first direction in theregion, and wherein, in the region, the line width of the gate driveline for the first transfer transistor and the line width of the gatedrive line for the overflow transistor are greater than a line width ofthe gate drive line for the selection transistor.
 3. The imaging deviceaccording to claim 1, wherein, in the region, the line width of the gatedrive line for the first transfer transistor and the line width of thegate drive line for the overflow transistor are greater than a linewidth of a gate drive line for the second transfer transistor.
 4. Theimaging device according to claim 1, further comprising: a first pixel;and a second pixel provided adjacent to the first pixel, wherein theregion is provided between a first photoelectric converting unit of thefirst pixel and a second photoelectric converting unit of the secondpixel in the planar view.
 5. The imaging device according to claim 2,further comprising: a first pixel; and a second pixel provided adjacentto the first pixel, wherein the region is provided between a firstphotoelectric converting unit of the first pixel and a secondphotoelectric converting unit of the second pixel in the planar view. 6.The imaging device according to claim 1, wherein the gate drive line forthe first transfer transistor is positioned closer to the photoelectricconverting unit than the gate drive line for the reset transistor is. 7.The imaging device according to claim 1, wherein the gate drive line forthe overflow transistor is positioned closer to the photoelectricconverting unit than the gate drive line for the reset transistor is. 8.The imaging device according to claim 1, wherein the imaging device isof front side illumination.
 9. The imaging device according to claim 1,wherein another line is positioned between the gate drive line for thefirst transfer transistor and the gate drive line for the secondtransfer transistor.
 10. The imaging device according to claim 9,wherein the gate drive line for the reset transistor is positionedbetween the gate drive line for the first transfer transistor and thegate drive line for the second transfer transistor.
 11. The imagingdevice according to claim 9, wherein one of a gate drive line, a powersupply line, a ground line for a selection transistor is positionedbetween the gate drive line for the first transistor and the gate driveline for the second transistor.
 12. The imaging device according toclaim 1, wherein another line is positioned between the gate drive linefor the first transfer transistor and the gate drive line for theoverflow transistor.
 13. The imaging device according to claim 12,wherein the gate drive line for the reset transistor is positionedbetween the gate drive line for the first transistor and the gate driveline for the overflow transistor.
 14. The imaging device according toclaim 12, wherein at least one of the gate drive line for a selectiontransistor, a power supply line, and a ground line is positioned betweenthe gate drive line for the first transfer transistor and the gate driveline for the overflow transistor.
 15. The imaging device according toclaim 1, wherein another line is positioned between the gate drive linefor the overflow transistor and the gate drive line for the secondtransfer transistor.
 16. The imaging device according to claim 1,wherein the region and the carrier accumulating portion overlap witheach other in the planar view.
 17. The imaging device according to claim1, wherein the gate drive line for the first transfer transistor, thegate drive line for the reset transistor, and the gate drive line forthe overflow transistor extend in the first direction in the same wiringlayer.
 18. The imaging device according to claim 2, wherein the gatedrive line for the first transfer transistor, the gate drive line forthe reset transistor, the gate drive line for the overflow transistor,and the gate drive line for the selection transistor extend in the firstdirection in the same wiring layer.
 19. The imaging device according toclaim 1, wherein, in the region, the line width of the gate drive linefor the first transfer transistor is greater than the line width of thegate drive line for the overflow transistor.
 20. The imaging deviceaccording to claim 1, wherein the first direction is a row direction.